The present invention relates to a heat and pressure type fixing device, and an electrophotographic system employing image forming apparatus, such as a copier, a printer, a facsimile, etc., including the fixing device.
In a conventional color electrophotographic system, a fixing device frequently provides brilliance to an image carried on a sheet similar to that of the background of the sheet.
To increase the brilliance of the image using the color-fixing device, fixing calorie is generally supplied by either increasing a fixing temperature or decreasing a line speed of a sheet of a printing member P. Because, a toner image can be made into a gel state and the toner particle loses its shape. However, when the fixing temperature is increased, heat diffusion from the fixing device increases. When the line speed is decreased, power is increasingly consumed due to a large amount of heat-supply not only to the toner but also the sheet. Such a usage of heat energy for the purpose of smoothing the toner surface is against a recent technical tendency of saving power.
It is known that brilliance highly likely increases as pressure increases at a nip where both the pressure and heat are applied to a sheet in the fixing device.
Thus, to provide the high brilliance, a system of creating a high nip pressure is demanded. As a result, a fixing device becomes bulky especially when improving productivity with the system. In addition, the line speed is decreased to supply a large amount of calorie when the brilliance is applied. Then, the productivity can significantly decrease as a result.
The Japanese Patent Application Laid Open Nos. 63-192068 and 2003-167459 propose a technology capable of controlling the brilliance by selectively using plural fixing devices. Specifically, such fixing devices include nip sections in the respective fixing devices, and convey sheets by primary drive rollers arranged therein. However, sheet jam and/or wrinkle occurs between the fixing devices or the sheet bends therebetween and contacts a guide member, so that an image is disturbed and a quality sometimes deteriorates.